All sexually reproducing organisms rely on meiosis to generate gametes, haploid cells containing one complete set of chromosomes. Central to this process is a reductional division, during which homologous chromosomes segregate to opposite spindle poles. Accurate segregation of chromosomes during meiosis is vital for the development of a fertilized embryo and for propagation of a species. To segregate faithfully away from its homologous partner, each chromosome must first find its proper partner, align with it along its entire length, and form a physical linkage through the act of meiotic crossing-over, or genetic exchange. Somehow meiotic chromosome interactions are governed to ensure that meiotic crossing-over occurs only between appropriate homologous partners, while inappropriate recombination events are prevented. In higher eukaryotes these interactions are clearly regulated at a level beyond mere sequence homology, since homologous sequences on nonhomologous chromosomes are normally precluded from synapsing and undergoing exchange. In C. elegans, chromosomes lacking special cis-acting sites known as "Pairing Centers" fail to undergo crossing-over and segregate at random, probably because they are unable to synapse. Thus, the Pairing Centers play a major role in governing inter-homolog interactions during meiosis. Pairing Centers have been roughly mapped on each chromosome, but no detailed information about their function exists. Combining the molecular and cytological tools available in C. elegans, we will define and characterize the molecular components underlying the role of Pairing Centers in meiotic chromosome behavior. First, we will delimit the sequence components that give rise to Pairing Center function. Second, we will identify proteins that associate with the Pairing Center and characterize their roles in ensuring proper meiotic chromosome organization. Third, we will use cytological methods to determine the role of the Pairing Center in meiotic chromosome pairing and synapsis.